Two-cavity MEMS variable capacitor for power harvesting

Novel 2 × 2 mm2 MEMS capacitive plates with two cavities (two capacitors) have been designed, modeled and fabricated for power harvesting by utilizing residual mechanical vibration in the environment using the electrostatic mechanism. The device is unique in the use of an innovative two-cavity design and electroplated nickel as the main structural material. When the capacitance increases for one capacitor, it will decrease for the other. This allows us to use both up and down directions to generate energy. The two-cavity design has achieved higher average power than conventional single-cavity devices under a wide range of vibration frequencies and amplitudes based on the time-domain simulations using Matlab. The movable plate was designed to vibrate without deformation and with resonance frequencies of around 900 Hz and lower using COMSOL finite element tool. The prototype two-cavity MEMS variable capacitor has been successfully fabricated using surface micromachining. The initial testing to investigate the electrical dynamic behavior and power generation from the fabricated devices was also implemented.